View transmission system



pril 17, 1934. H. :AMS 1,955,332

VIEW TRANSMISSION SYSTEM Filed March 5, 1930 Har/ey Jams.

l O ATTORNEY .Patented Apr. 17, 1934 VIEW TRANSMISSION SYSTEM Harley'lams. San Diego, Calif., assignor to Westinghouse Electric & Manufacturing Company,

a corporation of Pennsylvania Application March 5, 1930, Serial No. 433,338

' 4 Claims.

My invention relates to view transmission systems and it has particular relation to viewreceivers of the type wherein cathode-ray tubes are employed.

In the copending application of V. K. Zworykin, Serial No. 376,117, filed July 5, 1929, is disclosed an improved view-transmission system wherein synchronism between a scanning device at a sending station and an analogous device, comprising a cathode-ray tube, at a receiving station is automatically maintained.

In the said system, a single radio-channel is utilized for the transfer, from the sending station to the receiving station, of all of the frequencies necessary to transmit the View and to maintain automatic synchronization.

At each receiving station is disposed a cathoderay tube having therein a plurality of ray-controlling elements. One of the control-elements functions to modulate the intensity of the ray in accordance with the received view-frequencies, others function, under the control of one of the received synchronizing frequencies, to determine the speed of the horizontal-scanning movement of the cathode-ray, while still others of the said elements are periodically energized and deenergized, in response to groups synchronizing-frequency impulses to determine the travel of the ray in a vertical direction.

The synchronizing frequency first referred t is the frequency of horizontal movement of a scanning ray transversely of a moving motionpicture lm, at the sending station, and the periodicity of the second mentioned groups of impulses is determined by the rate of movement of the said illm.

In the operation of a view-transmission system of the type briefly described above, I have noted that the details of the received view, as seen upon the uorescent screen of the cathode-ray tube, are more perfect in the center of the screen than they are adjacent `to the right and left-hand boundaries thereof.

After careful investigation of the phenomenon of variation in detail I have determined that it arises by reason of the fact that, since the cathode-ray, in its movement from side to side, traces a sinusoidal curve upon the screen the successive transverse elements of the said curve, or scanning lines as they will hereinafter be designated,

are not parallel to each other.

It is, accordingly, an object of my invention to provide, in a view receiving system, means whereby uniformity of detail of a received-view shall be obtained,

Another, and more specific object of my invention is to so improve a view receiving system, of the type, disclosed in the aforementioned application of V. K. Zworykin that each scanning line, in the receiving tube, shall faithfully reproduce the corresponding scanning line at a transmitting station. 1

In short, my invention consists in providing means whereby the cathode-ray, instead of tracing a sinusoidal curve upon the fluorescent screen of the receiving tube, is constrained to move transversely thereof in a sinuous path the elements of which are parallel to each other for the greater portion of their length. The desired result is obtained by superimposing a locally derived potential, at twice the scanning frequency, upon the control-elements of the tube that determine the vertical travel of the ray, whereby the said ray, as it reaches the end of each transverse swing, quickly moves, in a vertical path, a distance corresponding to a predetermined spacing between successive scanning lines.

The novel .features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment, when read in connection with the accompanying drawing, in which Figure 1 is a schematic view of a complete viewreceiving station organized in accordance with my invention, and

Figs. 2, 3. 4 and 5 are diagrams to which reference will hereinafter be made in describing the method of operation of the system illustrated in Fig; 1.

Theapparatus illustrated in Fig. l of the drawing comprises an energy receptor constituted by an antenna l, a tuning condenser 2, an inductor 3 and a ground connection 4. The energy receiving circuit is coupled to a radio frequency amplifier 5, of any suitable type, which amplifier is followed by a. detector and audio frequency amplifier 6. The output from the audio fre-` quency amplifier is impressed upon a filter 7 that passes the vertical-framing frequency .impulses only, through an amplifier 8, to the primary wind-x. ing of a transformer 10, a second lter 11 andan amplifier 12, that pass the horizontal-scanningH frequency, and upon a lter 13 that permits they passage of all frequencies except the horizontal-"f scanning frequency, to the primary winding o an audio-frequency transformer 14.

The receiving system further comprises a cathdde-ray tube 15 of the type having a thermion c cathode 16, a control electrode 17, an anode 18, a ray-focusing conductive coating 20, a plurality of plates 21 and 22 for deilecting -the cathode ray in a vertical direction, and a plurality of coils 23 and 24 for defiecting the ray transversely of a fluorescent screen at the scanning frequency.

The control electrode 17 of the tube is connected to the cathode thereof through a source 25 of biasing potential and the secondary winding of the transformer 14, while a common source 26 is provided for the anode and the focusing element 20.

Although I have shown the ray deflecting plates and coils as disposed exteriorly of the tube it is to be understood that they `may be supported in the interior thereof if desirable.

The potential gradient between the control electrode of the cathode ray tube and the cathode comprises two components, a unidirectional potential from the biasing source 25, and an alternating potential, representative of the incoming view derived from the transformer 14. Since the magnitude of the electron stream between the cathode and the anode is a function of the potential between the control electrode and the cathode, and since the brilliance of the fluorescence of the screen at the end of the tube is at every instant a function of the magnitude of the stream, or cathode-ray, passing through the anode, the said brilliance is always proportional to the amplitude of the alternating potential representing the incoming View.

If, therefore, the cathode ray is caused to traverse thel fluorescent screen synchronously with the traversing of a moving picture lm at the transmitting station by a scanning light ray, or the scanning by a cathode-ray, at the transmitting station, of a photo-sensitive screen upon which a view is focused, the lin or view will appear upon the said fluorescent screen and will convey the illusion of motion.

Synchronism between the horizontal movement of the cathode ray and the movement of the scanning ray at the transmitting station is ob-` tained by impressing the scanning frequency, preferably 480 .to '150 cycles per second, upon the carrier at the transmitting station and, at the receiving station, after ltering it out from the incoming signals, by applying it across the coils 23 and 24.

In order that the cathode-ray, in the receiving tube, shall move vertically from the top to the bottom of the fluorescent screen during the exact time interval required for one complete pictureframe of a motion-picture film to pass beforegthe scanning ray at the transmitting station, and shall return to its initial position at the tcp of the screen before lthe next frame encounters the transmitting ray, means are provided whereby the potential across the deflecting plates 2l and 22 progressively passes from zero to maximum and abruptly returns to zero.

In the aforementioned Zworykin application the deflecting plates, controlling the vertical movement of the cathode ray, are described as being charged at a constant rate through a rectifying device, and a grid-glow tube is provided whereby incoming impulses, having an arbitrary tone-frequency of 1200 cycles per second and a group-frequency determined by the rate of advance ofva lm at the transmitting station, cause the periodical discharge of the plates.

The rate of charge and discharge of the deflecting plates, in the Zworykin system, is graphically shown by Fig. 2 of the drawing. wherein the Y- axis represents potentials and the X-axls represents time. The distribution of the scanning lines upon the fluorescent screen, in the said system, with the spacing between successive lines greatly exaggerated, is exemplified by a sinusoidal curve 30 in Fig. 3 of the drawings, from which it will be noted that the lines are spaced apart, adjacent to the margins of the screen, differently than they are spaced along a median line E-E, as indicated by the points A-B and C-D on the curve.

The manner in which I am enabled to attain parallelism of the scanning lines and the consequent imprrvement in detail of the received view will now 1e explained.

Referring again te Fig. l of the drawing, itl

will be noted that the deecting plate 22 is directly connected to ground and that the opposite plate 21 is connected to the anode 31 of the thermionic rectifying device 32 that is provided with a control electrode 33 and has a cathode 34 that is also` connected to ground through a source 35 of high potential. A condenser ,36 is connected in shunt relation to the deflecting plates 21 and 22, which condenser, therefore, is serially connected between the positive terminal of the potential source 35 and the anode 31 of the rectifying device 32.

The control electrode 33 of the rectifying device is connected to the cathode thereof through the secondary winding of an audio frequency transformer 3'7 and a source 38 of biasing potential is supplied for normally biasing the control electrode to the cut-off point.

The secondary winding of the audio frequency transformer 37 is supplied with alternating potential at twice the scanning frequency, namely at 960 to 1500 cycles, for a purpose that will, hereinafter, be explained in more detail.

A short-circuiting device 40 is provided, the said device, preferably, taking the form of 'a thermionic tube 41 having a cathode 42, an

anode 43 and a control electrode 44. A conducttor 45 extends between the cathode of the shortcrcuiting device andthe anode of the rectifying device 32 and the anode of the short-circuiting device is connected to a ground connection 46 common to one plate of the condenser 36, the positive terminal of the source 35 and the deflecting plate 22.

The input circuit of the rectifying device is constituted by the secondary winding of the transformer 10, the primary winding of which is energized through the framing-frequency filter 7, and a biasing potential source 47 is provided for normally biasing the control electrode of the short-circuiting device to the cut-0H point.

In the operation of my improved view-receiving system, the incoming carrier-wave, which is modulated according to the picture-element intensity, the scanning-frequency and the recurrent groups of framing-frequency, is demodulated, and the derived audio-frequencies are routed, through the filters 13, 11 and 7 to the control element of the cathode-ray tube, the deflection coils 23 and 24, and to the short-circuiting device 40, respectively.

The deflecting coils cause the ray to swing from side to side of the fluorescent screen, at the scanning frequency, and the rate of movement of the ray, vertically of the screen, is proportional to the charging of the deflecting plates 21 and 22 through the rectifying device 32.

Since it is an object of my invention to have the scanning lines parallel, upon the fluorescent screen, means must be provided whereby the potential across the deflecting plates is not increased during a single traverse of the cathode ray. To this end the biasing source 38 is so adjusted that the Vnegative potential applied therefrom to the control-electrode 33 is suiiicient, normally, to prevent the flow of space current through the rectifying device. 36, however, must receive an increasing charge if the cathode-ray is to move from the top to the bottom of the fluorescent screen, and each increment of the charge, if the scanning lines are to be parallel, must occur only at the end of Veach traverse.

The amplitude of the potential supplied to the control electrode of the rectifying device, therefore, from the 960 to 1506 cycle source, is so adjusted that the peak of each positive half cycle serves to overcome the normal biasing potential on the control-electrode 33 and permits the rectifying device to become momentarily conductive whereby the charge upon the condenser 36 is periodically increased by small increments.

Since the scanning frequencyhas been indicated as preferably being from 480 to 750 cycles, and thecharge controlling frequency as corresponding to the time required for the scanning ray at the transmitting station to completely explore a single frame of the film the cathode ray is returned to its initial position through the action of the short-circuiting device 40, the electrodes of which are connected in shunt relation to the deiiecting plates and the condenser 36. The short-circuiting action is accomplished by reason of the fact that each group of incoming oscillations, at the framing frequency, causes the grid of the short-circuiting device to become suiliciently positive for the said device to become conductive.

It will be apparent, from a consideration of the foregoing description of a view-.receiving station organized in accordance with my invention, that the received view, as seen upon'the fluorescent screen, is equally as well defined adjacent to the edges of the screen as it is in the center. 'I'his feature is highly important if the view is enlarged and thrown upon a screen since the enlargement accentuates every deficiency thereof.

Numerous modifications of my invention will be apparent to those skilled in the art. For example, the grid-control of the rectifying device may be dispensedwith andperiodical anode potential may be applied thereto through the medium of a commutating device of a suitable type. The commutating. device may either apply the anode/potential iirectly from. a suitable source The condenser A through a current-limiting device or it may permit the discharge of an auxiliary condenser having the proper capacity to add the necessary charge-increments to the deflection control condenser 36.

Furthermore, the connections to the deilecting .plates may be reversed and the ray may be caused to ymove from the bottom to the top of ,the nuorescent screen instead of from top to bottom as hereinbefore described.

In addition, it should be clearly understood that my improved receiving system is not limited to the reception of fllm-facsimiles. "That is, the incoming signals may have their origin in a direct-view transmitting station of the type wherein a scanning-ray, electronic or light, is utilized to explore the elements of Van object or of an image of an' object. In such event the impulses corresponding to the groups of oscillations at the framing-frequency, representing the travel 'of the ray in a direction perpendicular to the scanning direction, are not derived under the control of movements of the object or image being "televised" but are introduced into the carrier by other suitable means.

I also wish to emphasize the fact that it lies within the scope of my invention to use a lightray at a receiving station and, by the use of control means somewhat analogous to those hereinbefore described, to cause the said light-ray to traverse a screen in parallel lines.

My invention, therefore, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

l. In a system of the television type. mea for causing a scanning medium to traverse a screen in a path substantially parallel to one axis of the screen, means for progressively shifting the path of travel of said scanning medium, said means comprising a condenser and a charging circuit therefor, and means for periodically interrupting the charging current to said condenser during the intervalof travel of said scanning element across substantially the whole of said screen.

2. In combination, means for producing a variable potential having a substantially straight line wave front characteristic and means for periodically modifying said wave front to produce a step-like formation.

3. In combination, means for producing a variable potential having a substantially .straight line wave form characteristic and means for periodically modifying said variable potential at a. plurality o fpoints along its straight line wave form characteristic said modifying means producing a step-like characteristic in -the modified a scanning point, means for shifting the path of travel of said second scanning point in accordance with a movement of an object at said transmitting end, said means comprising a condenser Aand a charging circuit therefor under the control of said object at the transmitting end. and means for periodically modifying the charging current to said condenser to define horizontal parallel paths of travel of said second scanning point. 

